High expansion ratio, well-defined cell structure, and an excellent flame retardant characteristic are essential properties for broadening the applications of polymeric foam. In this study, by applying microcellular foaming technology using compressed CO, as the blowing agent, we are challenged to synthesize the desirable poly(lactic acid) (PLA) foams with phosphorus-containing flame retardant (FR) and starch as the natural charring agent. It was interesting to find that the introduction of 15-25 wt % FR increased the limiting oxygen index (LOI) of PLA foams from 18.2% to 24.8-28.4% and simultaneously increased the foam expansion of PLA foams from 4.4 to 7.5-16.0. The addition of starch with Content of 1-5 wt % further increased the LOT up to 30.6% and also endowed PLA/FR/St foams with improved antidripping properties. All these wonderful characteristics make the prepared PLA foams very promising for application in green packaging.